function animate(obj,target,callback){
    clearInterval(obj.timer);
    obj.timer = setInterval(function(){
    var step =(target - obj.offsetLeft )/10;
    step = step > 0? Math.ceil(step):Math.floor(step);
    if(obj.offsetLeft == target){
        //清楚定时器
        clearInterval(obj.timer);
        if (callback) {
            callback();
        }
    }else {
        obj.style.left = obj.offsetLeft + step +'px';
    }
},50)
}